I don't think Nate switched teams, I think he just asked to train with Penn while Jens trains his opponent in Corey Hill. Who would want their next opponent standing 8 ft. away from them, watching everything they do? It only makes sense for this specific situation (two members of the same team fighting). I think the whole "traitor" talk and Manny flipping him off will turn out to be in jest.
With Gray and Lauzon already advanced, it wouldn't make sense for Nate to burn the Team Pulver bridge. Although, this time Nate's working with BJ, will give Maynard, Lauzon, and Wiman all a chance to scout him...
I don't think Nate would need any help for Corey though, Corey is just too raw. With two fights next week I assume one ends rather quickly, I'm guessing a quick sub from Nate. Though Manny/Wiman could end rather quickly as well.
i'm a monster
i'm a maven
i know this world is changin'
never gave in
never gave up
i'm the only thing i'm afraid of